The present invention relates to an oxygen-absorbing resin composition used as a packaging material for contents quite susceptible to deterioration in the presence of oxygen, in particular, beverages, foods, pharmaceutical agents or the like.
As packaging containers, there have conventionally been used, for instance, metallic cans, glass bottles and various kinds of plastic containers. The plastic containers have such advantages that they are light-weight and excellent in the impact resistance to some extent, but they suffer from various problems such that the contents packaged therein are deteriorated due to the oxygen gas possibly passing through the walls of the containers and that they undergo the reduction of their flavor. In case of, in particular, the metallic cans and the glass bottles, the permeability to oxygen gas is almost zero and only the oxygen remaining in these containers would contribute to, for instance, the deterioration of the contents thereof, while in case of the plastic containers, an amount of oxygen which cannot be disregarded may permeate through the walls thereof and accordingly, the plastic containers suffer from a problem that the shelf stability of the contents thereof is quite low.
To solve such problems associated with these plastic containers, there has been proposed the use of multi-layer structures each having at least one layer of a resin having gas-barrier properties such as an ethylene-vinyl alcohol copolymer (see, for instance, Japanese Un-Examined Patent Publication Hei 1-278344).
In addition, there has also been proposed a composition comprising a polymer and having oxygen-trapping properties or a barrier for packaging, which comprises a layer of such a composition, wherein the composition traps oxygen through the oxidation of an oxidizable organic component with a metallic catalyst and a polyamide, in particular, a xylylene group-containing polyamide is used therein as such an oxidizable organic component (see, for instance, TOKUHYO Hei 2-500846).
In this respect, the foregoing resin excellent in the gas-barrier properties such as an ethylene-vinyl alcohol copolymer (EVOH) suffers from such a problem that it shows quite excellent oxygen-barrier properties under the low-humidity conditions, but it has an extremely high permeability to oxygen under the high humidity conditions. Furthermore, the foregoing gas-barrier resin has frequently been used in combination with the heat-sterilization/packaging technique such as the hot water-sterilization technique, the sterilization technique through boiling, and the retort-sterilization technique for the improvement of the shelf stability of the contents of the packages. Accordingly, EVOH is exposed to high-humidity conditions during the heat-sterilization process. For this reason, not only it is thus in the state having a high oxygen-permeability, but also the state thereof having a high oxygen-permeability is continuously maintained even after the completion of the sterilization treatment and therefore, it would be impossible to ensure the desired barrier properties.